Petroleum refining begins with the distillation or fractionation of crude oils into separate hydrocarbon groups. The resultant products are directly related to the characteristics of the crude processed. Most distillation products are further converted into more usable products by changing the size and structure of the hydrocarbon molecules through cracking, reforming, and other conversion processes. These converted products are then subjected to various treatment and separation processes such as extraction, hydro-treating, and sweetening to remove undesirable constituents and improve product quality.
Treating petroleum products with acid is a procedure that has been used for more than a century in the petroleum industry. Until circa 1930, acid treatment was almost universal for all types of petroleum products, especially for cracked gasoline, kerosene, and lubricating stocks. Various acids have been used, but sulfuric acid is the most advantageous. The reactions of sulfuric acid with petroleum fractions are complex. The undesirable components to be removed are generally present in small amounts, requiring large excesses of acid for efficient removal.
Sludge produced from the acid treatment of petroleum distillates, even gasoline and kerosene, is complex in nature. Esters and alcohols are present from reactions with olefins; sulfonation products from reactions with aromatics, naphthenes, and phenols; and salts from reactions with nitrogen bases. In addition, naphthenic acids, sulfur compounds, and asphaltic material are all retained by direct solution. Added to the mix are various products of oxidation-reduction reactions, such as coagulated resins, soluble hydrocarbons, water, and free acid.
The waste product that remained behind after filtration was customarily disposed of in open lagoons. The physical and chemical characteristics of this sludge generally vary with depth and from lagoon to lagoon. Sludge resulting from the treatment of gasoline and kerosene, so-called light oils, separates as a tar-like material. Sludge from heavy oil and bitumen, however, separates as granular semisolids. After decades within these lagoons, the materials range from a solid, charcoal-like material at the bottom to a liquid mixture of sulfuric acid, other acidic waste products, and rainwater at the surface. At other times these lagoons can be very heterogeneous with various stratifications of acidic waste materials.
Treating these acidic waste products is difficult due to a number of factors. First, as previously described, the waste is very complex. As understood in the art, the waste composition varies from one area of a lagoon to another, and often from one depth to another within the same area in a lagoon. Second, the acid content of the waste also varies. As an example, the acid content of the waste most often ranges from less than one to fifty percent, however, some highly acidic waste consists of as much as ninety percent acidity. Third, when these acidic materials are disturbed, dangerously high concentrations of acid gases can be emitted, primarily sulfur dioxide and, to a much lesser extent, hydrogen sulfide.
Conventional methods for remediation of highly contaminated acidic waste sites is inefficient, ineffective, dangerous, and costly. Typically, remediation efforts begin by measuring the pH of the waste at a few points throughout the contamination site. Samples of the waste are then taken and the amount of neutralization reagent is determined using empirical methods of trial and error. As known in the art, many of the contamination sites remain untreated due to ineffective measurement and treatment processes currently available. For example, if insufficient neutralizing agent is applied, sites generally require re-treatment even after the pH has increased following an initial treatment due to the delayed ionization of certain acid contaminants. More problematic situations arise because current measurement and treatment protocols are often grossly inadequate for handling highly contaminated acidic waste sites, thereby emitting dangerous acid gases. Such sites typically require evacuation or costly containment efforts when gases are emitted during waste disturbing remediation activities. It is well known that contracts to remediate such sites have been breached or go unfulfilled due to financial exposure and other liabilities that result for failing to suitably remediate a contaminated site. A commercially-viable means to safely and efficiently treat these acidic wastes without emitting dangerously high concentrations of acid gases is needed.